Uncoupling device for connecting a drilling tool to the end of a drilling column and a drilling system comprising such an uncoupling device

ABSTRACT

Collection device for connecting a drilling tool, such as a bit, to the end of a drilling column, in which the connection device comprises a first element, with a first end, intended to be connected to the end of the drilling column, and a second element, with a second end, intended to be connected to the drilling tool, in which the second element is fixed to the first element so as to allow a translational movement in a longitudinal direction in order to make it possible to change the distance between the first end and this second end, characterized in that the connection device comprises a “pusher” structure for transmitting a thrust force from this first element towards the second element, comprising a set of “Belleville” washers making it possible to ensure that said thrust force, from the first element toward the second element, is substantially constant in any position of the second element with respect to the first element.

The present invention relates to an uncoupling device for connecting a drilling tool, such as a bit, to the end of a drill string, wherein the uncoupling device comprises a first element, with a first end, intended to be connected to the end of the drill string, and a second element, with a second end, intended to be connected to the drilling tool, wherein the second element is fixed to the first element so as to allow a translational movement, in a longitudinal direction in order to make it possible to change the distance between this first end and this second end.

The uncoupling device according to the invention is used for connecting a drilling tool, such as a bit, to the end of a drill string. The assembly, composed of a drill string and a drilling tool connected to the end thereof, is used in the drilling of wells such as wells for crude oil production. It is possible to connect the drilling tool directly, but the device may also be connected to a downhole motor, to which the drilling tool is connected, or even to the measurement system (MWD), to which the downhole motor and the drilling tool is connected.

The drilling tool is guided towards the bottom of the well thanks to the drill string. The drill string rotates and this rotation is transferred to the drilling tool. In addition, the drill string is used to push the drilling tool, with sufficient force, against the geological formation to create the well.

When drilling a well, the quantity of pipes required for forming the dril string is dependent on the depth of the well in relation to the surface. The deeper is the well, the greater is the quantity of tubes required and the greater is the mass of the drill string. If the well is deviated, the quantity of tube is also greater. It is possible to have significantly deviated wells (10 km or more) which are “only” 2 or 3 km deep.

In order to adjust the force applied with the drill string on the drilling tool, the operator actuates, by means of a control system, during the drilling of the well, the descent of the drill string so as to adjust this force on the drilling tool.

The control system used for controlling this force comprises, for example, a brake at the wellhead. The effect of this measure consists in that the drilling tool therefore only supports a small portion of the weight of the drill string.

A well-known phenomenon is that the drilling tool attacks geological structures with a variable hardness. The variation in the hardness of the geological structures encountered by the drilling tool gives rise to reactions, in the assembly of drill string/drilling tool. These reactions are sources of such significant vibration that they may have a major influence on the service life of the drilling tool.

For example, when the drilling tool attacks a rock of a hardness very superior to the average hardness of the geological formations, it bears a very significant reaction effect in a longitudinal direction towards the wellhead. The repetition of these reaction loads causes wear of the drilling tool. The process for replacing such a drilling tool is relatively long and costly. For this reason, it is necessary to control the vibration level generated on the drilling tool so as to extend the service life of said drilling tool.

The present invention aims to limit the high reaction constraints and vibrations generated by these reaction constraints on the drilling tool in the longitudinal direction of the wellbore.

The present invention relates to an uncoupling device for connecting a drilling tool, such as a bit, to the end of a drill string, wherein the uncoupling device comprises a first element, with a first end, intended to be connected to the end of the drill string, and a second element, with a second end, intended to be connected to the drilling tool, wherein the second element is fixed to the first element so as to allow a translational movement, in a longitudinal direction for allowing to modify the distance between this first end and this second end, characterized in that the uncoupling device comprises a “pusher” structure for transmitting a compressive force from this first element towards the second element, comprising a set of “Belleville” washers, designed and used in the operating range thereof such that they allow to ensure that said compressive force, from this first element towards the second element is substantially constant in any position of the second element with respect to the first element.

In other words, in the longitudinal direction of the well, the uncoupling device according to the invention allows some translational movement of the drilling tool in relation to the drill string so as to prevent excessive pressures on the drilling tool and prevent any vibrations applied on said drilling tool. In this way, the reaction force from the geological formation on the drilling tool is self-regulated by means of the uncoupling device. The drilling tool is no longer submitted to repeated extreme reaction constraints and wears less quickly.

An additional technical effect of these measures is that the drill string and the drilling system are submitted to less parasitic vibrations, facilitating well drilling control.

According to the invention, the force between the first element and the second element of the uncoupling device is obtained using a set of “Belleville” washers. A reference to “Belleville” washers has already been made in the prior art under the term “spring washers” or “elastic washers”.

The “Belleville” washer is a washer performing a spring function. One of the important features of “Belleville” washers lies in the low cost thereof. They offer the advantage that they can be associated in various manners, making it possible not only to obtain the stiffness wished for the assembly, but also to create systems having a “variable stiffness”.

According to one preferred embodiment, said compressive force is provided with an acceptable tolerance range of maximum 20%, but preferably maximum 10%, ideally of maximum 2%.

According to one preferred embodiment, the device is an uncoupling device wherein the “pusher” structure comprises a set of “Belleville” washers positioned in relation to each other so as to form a stack of washers.

In this design, the various “Belleville” washers are positioned with the first one in one position, the second one in an inverted position relative to the first one, the third one in the same position than the first one, the fourth one in the same position than the second one and so on. In this way, a spring offering a constant “spring” feature is obtained. In a “column” design, the displacement distance between the first and the last washer of a set is maximal.

According to one preferred embodiment, the washers are positioned so as to obtain a pack of washers.

In the “pack” design, all the washers are positioned in succession in the same direction. In this way, a very high-strength spring is obtained and the displacement distance between the first and the last washer of a set is minimal.

According to one preferred embodiment, the “pusher” structure comprises a plurality of modules mounted in sequence, in the longitudinal direction, between the first element and the second element, each module being suitable for transferring a portion of the compressive force from this first element towards this second element, so that the sum of said portions of the compressive force of the modules is equal to the compressive force of the “pusher” assembly.

According to one preferred embodiment, the device is provided with “locking” elements adapted for locking the functionality of at least one module for allowing to the unlocked modules only to transfer the compressive force from the first element to the second element. The locking system is used to prevent excessive compression of the “Belleville” washer. In this way, it ensures operation only in the zone wherein the force supplied by the “Belleville” washer is constant or substantially constant.

For example, a first module may be suitable for absorbing a force of up to a maximum of 100,000 Newton, a second module being suitable for absorbing a force of up to a maximum of 150,000 Newton and a third module being suitable for absorbing a force of up to a maximum of 200,000 Newton.

Depending on the geological structures wherein the drilling tool is used for drilling a well, one or a plurality of modules may be set so as to obtain an optimal force feature in the device according to the invention.

According to a preferred embodiment, the modules of the plurality are identical, each of the modules supplying an identical portion of the compressive force.

According to a preferred embodiment, the modules are different so as to ensure that one of the modules is suitable for transferring a compressive force, with another magnitude than the one of the other modules.

According to a preferred embodiment, each module comprises an inner tube portion, and an outer tube portion surrounding the inner tube portion, and wherein:

-   -   the outer tube portions are rigidly connected in sequence with         each other and with the first element,     -   the inner tube portions are rigidly connected in sequence with         each other and with the second element, and     -   each module transfers said portion of the compressive force to         the inner tube portion of said module.

According to a preferred embodiment, the “pusher” structure is housed in an annular volume extending radially between an inner tube, for channelling at least one fluid inside said inner tube, and an outer tube, rigidly connected with the first element and encasing said “pusher” structure.

According to a second aspect of the invention, the present invention also relates to a drilling system comprising an uncoupling device, according to the invention, and further comprising:

-   -   a drill string comprising at least one pipe, said drill string         being connected to the first element of the uncoupling device,     -   a drilling tool, such as a bit, for drilling a geological         formation, the drilling tool being connected to the second         element of the uncoupling device, and     -   a device for retaining the drill string, at the head of the         wellbore, adapted for controlling the movement of the drill         string downwards and upwards in the wellbore.

According to one preferred embodiment, the uncoupling device comprises at least one displacement sensor for determining the position of the second element relative to the first element over time so as to obtain the feed rate of the second element with respect to the first.

According to a preferred embodiment, the uncoupling device comprises a rotation, thrust measurement and torque measurement sensor for estimating the resistance of the drilled rock and the degree of wear of the drilling tool by means of a cutting model.

According to a preferred embodiment, the system according to the invention comprises an uncoupling device comprising at least one displacement sensor for determining a position of the second element relative to the first element, wherein the system comprises transmission means for transmitting said position of the second element to the retaining device for monitoring a retaining force of the drill string.

Since the compressive force towards the tool is constant, it is clear that the compression/tension state in the drill string is constant if the position at the surface is kept constant. The first element of the device thus has a fixed axial position in the drilled hole. Therefore, it can be used for measuring the axial displacement of the second element, and thus the feed of the drilling tool over time. If a rotation sensor is used with also axial and torque force sensors, it is possible to estimate the performance of the tool per revolution drilled. Indeed, the feed rate is obtained by means of the axial displacement of the second element and the rotational speed of the drilling tool. The drilling torque and the compressive force are also obtained. The performance and efficiency of the drilling tool can thus be readily calculated. On the basis of this cutting model well-known to those skilled in the art, it is also possible to estimate the resistance of the drilled rock, and the degree of wear of the drilling tool.

According to one preferred embodiment, the drill string retaining force is increased if the position transmitted to the retaining device indicates that the second element is in the vicinity of the first element, and the force of the drill string is reduced if the position transmitted to the retaining device indicates that the second element is far from the first element.

The present invention and the various advantages associated with this invention will be understood more clearly on reading the following with reference to the figures wherein:

FIG. 1 shows, schematically, the use of the device according to the invention during drilling of a well,

FIG. 2 shows, in detail, the two elements of the device according to the invention,

FIG. 3 shows, schematically, the set of washers, in the “column” design,

FIG. 4 shows, schematically, a set of washers, in the “pack” design,

FIG. 5 shows the embodiment between force and displacement for “Belleville” washers,

FIG. 6 shows, schematically, the presence of a first, a second and a third module, each module comprising a set of washer,

FIG. 7 shows a set of washers in the “column” position with, between two elements, one element for limiting the displacement of a first washer with respect to a second washer,

FIG. 8 shows “trapezoidal” shaped washers; and

FIG. 9 shows two washers provided with lips for limiting the deformation of each washer.

FIG. 1 shows, schematically, a drilling system 1 according to the invention. The drilling system comprises a rig or derrick 2 which are positioned on the ground at the location where the well 3 is to be based.

On the rig 2, an element 4 is provided and allows connecting a first end of a drill string 5. The upper end of this drill string 5 is connected to the device 4. The user may, using the device 4, control the movement of the drill string 5 downwards or upwards inside the wellbore 2.

The device 4 is also provided with driving means for rotating the drill string 5. The downwards and upwards movement of the drill string 5 are controlled by retaining device 6 directly connected to the device 4, for example by means of a cable.

A drilling tool 7 is present at the lower end of the drill string 5. This drilling tool 7 may be, for example, a PDC type drilling tool. Such a type of drilling enables a relatively easy estimation of the resistance of the rock. In other words, if a PDC type drilling tool is used, the resistance of the rock may be estimated while the drilling tool is in use. A device 10 according to the invention is inserted, between the end of the drill string 5 and the drilling tool 7, so as to ensure that the vibrations generated in the system, composed of the drill string 5, the drilling tool 7 and the intermediate device 10, can be controlled.

The presence of the device 10 according to the invention is important with respect to variations in the geological structures in the soil 8, the geological structure being those attacked using the drilling tool 7.

In practice, the mass of the tubes forming the drill string 5 may be very significant. For optimum operation and in order to suitably manage the wear of the drilling tool 7, the reaction force from the geological formation 8 onto the drilling tool 7 may be limited, so as not to exceed, for example, a value of 20 tonnes. Consequently, the value of the retaining force of the retaining device 6 is very high and is difficult to control.

Control difficulties depends on the length of the drill string 5 and also on the time interval required for reacting, with the retaining device, to the reactions submitted by the drilling tool 7.

The vibrations, the reactive forces generated by the impact of the drilling tool 7 on the geological formation 8, during the use of the system 1 according to the invention, are propagated by the tubes from the bottom of the well to the rig 2 of the system 1. These vibrations, these reactive forces are, as a general rule, used to control the retaining force value. However, such a propagation can by distributed over a long time interval, for example greater than 30 seconds for torque constraints for example. Control with the retaining device 6 is only possible with a significant time lag, which increases the difficulty in controlling the retaining force.

FIG. 2 shows an embodiment of the uncoupling device 10 according to the invention. The device 10 comprises a first element 11 adapted for being connected to the end of the drill string 5 (see FIG. 1). The element 11 is connected to a second element 12 which, at the end thereof, is adapted for attaching the drilling tool 7. It is important to note that the second element 12 may be moved in a longitudinal direction indicated under the reference “y”. This capability of translational movement in a direction “y” enables the modification of the maximum length, indicated under the reference “x” of the device 10 according to the invention. By means of this modification of the length, the device may react with respect to the reactions applied to the drilling tool 7 and generated by the geological formation 8.

The uncoupling device 10 according to FIG. 2 comprises an inner tube 13 for channelling, inside said tube 13, at least one fluid. In addition, the device 10 comprises an outer tube 14, rigidly connected to the first element 11 and acting as an outer casing for the uncoupling device 10 over, substantially, the entire length thereof in the longitudinal direction “y”. The inner tube 13 and/or the outer tube 14 may optionally be embodied by a set of sections so as to facilitate the assembly of the uncoupling device 10.

A spring, in the form of a set of “Belleville” washers, is provided inside the device 10, in order to adjust the translational movement of the second element 12 of the device 10, with respect to the first element 11 of the device 10, Herein, the term “Belleville” washer is used for a type of spring shown in FIGS. 3 and 4.

A first feature of the “Belleville” washers is that they are used for creating a spring function. A second feature is that the spring obtained has a low cost. It is important to be able to produce a plurality of types of “Belleville” washers according to the size thereof. The main dimensions of a “Belleville” washer are shown in FIG. 3. The “Belleville” washer has an inner diameter “d”, an outer diameter “D”, a thickness “e” and an unloaded height “h”.

The dimensions may be chosen so as to obtain a spring constructed using “Belleville” washers presenting a suitable deformation. According to the invention, the “Belleville” washers are produced and used within a deformation range so that they can provide, on the drilling tool 7, a constant compressive force. It means that the displacement of the element 12 with respect to the element 11 should be carried out while keeping the compressive force of the drilling tool 7 on the geological structure (see FIG. 1) substantially continuous. This option of keeping the compressive force constant requires limiting of the translational movements of the element 12 with respect to the element 11 (see FIG. 2) so that they are less than the maximum displacement allowed by the deformation of the washers used in the device 10.

FIG. 3 shows a set of washers 20, 21, 22, 23, 24 and 25. FIG. 3 also shows a mutually opposed washer stack. It means that a relatively large distance is obtained over which various assembled washers may be deformed. The deformation of the washers 20-25 is authorised until the force, applied on the set of washers 20-25, is so significant that the washers are deformed and the flattened shape thereof is obtained. One advantage of the invention lies in that, even if the force applied on the “Belleville” washers 20-25 is very significant, the deformation of the various washers 20-25 can no longer continue but said washers are pushed onto each other without being damaged. When the force is no longer applied on the set of washers 20-25, the functionality of the washers is guaranteed and the set of washers 20-25 can return to the initial shape thereof. In our case, it is necessary to ensure that the washer can no longer be compressed more than the maximum deformation continuing to provide a constant force.

FIG. 4 shows a set of “Belleville” washers in a “pack” design. The various washers 25, 26 and 27 are positioned in the same direction. The stiffness to which the set of washers 25-27 can be deformed is limited but the spring features of the set are very important.

The relationship between the displacement, i.e. deformation, and the force for various types of “Belleville” washers is shown in FIG. 5. For the uncoupling device according to the invention, it is advisable to ensure that the washer cannot be compressed more than the maximum deformation which always provides him a constant stress.

The operating mode of the “Belleville” washers is shown in FIG. 5, particularly the area 80 where the compressive force is constant for a certain deformation. This means that, if a “Belleville” type washer is chosen with a force/displacement feature according to the line 81, deformation situated inside the oval 80 is acceptable in order to ensure that the thrust is constant during the deformation indicated using this oval 80.

In practice and for the use of the present invention, a tolerance range may be accepted provided that it is situated between 20 and 50%. The most advantageous option would be that of accepting a tolerance range between 5 and 10%. Ideally, the most suitable tolerance range is situated around 2%.

FIG. 6 shows, schematically, a possible embodiment of a set of washers. FIG. 6 shows three modules I, II and III, wherein each of the modules comprises a set of “Belleville” washers. The configuration according to FIG. 6 may be used for example for adapting the device according to the invention to a specific use. The set I may be adapted, for example, for a deformation of up to 15 tonnes (150,000 Newton). The set II may be adapted, for example, for a deformation of up to 15 tonnes and the set III for a deformation of up to 20 tonnes (200,000 Newton). In the case where the user needs an assembly to receive 15 tonnes (150,000 Newton), it may for example lock the functionality of nodule I and III and merely make use of the “spring” features of module II.

A device comprising three modules is shown in FIG. 6. The device may comprise more than three modules. For example, in order to obtain a force of 100,000 Newton, it is necessary to arrange a plurality of modules (8 modules for example), because the realizable strains in the embodied dimensions are not sufficient with a single module.

FIGS. 7, 8 and 9 show various examples of “Belleville” washers with a specific use.

FIG. 7 shows two washers 31 and 32 with, between the two, an element 33 for limiting the maximum deformation of the washers 31 and 32.

FIG. 8 shows two washers 41 and 42 having a “trapezoidal” shape.

FIG. 9 shows two washers 51 and 52 provided, internally, with lips 61 and 62 suitable for minimising the deformation to be applied to the washers 51 and 52. 

1. Uncoupling device for connecting a drilling tool, such as a bit, to the end of a drill string, wherein the uncoupling device comprises a first element, with a first end, intended to be connected to the end of the drill string, and a second element, with a second end, intended to be connected to the drilling tool, wherein the second element is fixed to the first element for allowing a translational movement, in a longitudinal direction for allowing to modify the distance between this first end and this second end, characterized in that the uncoupling device comprises a “pusher” structure for transmitting a compressive strain from this first element towards the second element, comprising a set of “Belleville” washers, designed and used in their operating range thereof such that they allow to ensure that said compressive strain, from this first element towards the second element is substantially constant in any position of the second element relative to the first element.
 2. Uncoupling device according to claim 1, wherein said compressive force is provided with an acceptable tolerance range of maximum 20%, but preferably maximum 10%, ideally of maximum 2%.
 3. Uncoupling device according to claim 1, wherein the “pusher” structure comprises a set of “Belleville” washers positioned relative to each other so as to form a column of washers.
 4. Uncoupling device according to claim 3, wherein the washers are positioned relative to each other so as to obtain a pack of washers.
 5. Uncoupling device according to claim 2, wherein the washers are positioned so as to obtain columns of packs of washers.
 6. Device according to claim 1, wherein the “pusher” structure comprises a plurality of modules mounted in sequence, in the longitudinal direction, between the first element and the second element, each module being adapted for transferring a portion of the compressive strain from this first element towards this second element, so that the sum of said portions of the compressive strain of the modules is equal to the compressive strain of the “pusher” assembly.
 7. Device according to claim 6, wherein the device is provided with “locking” elements adapted for locking the functionality of at least one module for allowing to the unlocked modules only to transfer the compressive strain from the first element towards the second element.
 8. Uncoupling device according to claim 6, wherein the modules of the plurality are identical, each of the modules supplying an identical part of the compressive strain.
 9. Device according to claim 6, wherein the modules are different so as to ensure that one of the modules is adapted for transferring a compressive strain, with another magnitude than the one of the other modules.
 10. Device according to claim 6, wherein each module comprises an inner tube portion, and an outer tube portion surrounding the inner tube portion, and wherein: the outer tube portions are rigidly connected in sequence with each other and with the first element, the inner tube portions are rigidly connected in sequence with each other and with the second element, and each module transfers said part of the compressive strain to the inner tube portion of said module.
 11. Device according to claim 1, wherein the “pusher” structure is housed in an annular volume extending radially between an inner tube, destined to channelling at least one fluid inside said inner tube, and an outer tube, rigidly connected with the first element and encasing said “pusher” structure.
 12. Drilling system comprising an uncoupling device, according to claim 1, and further comprising: a drill string comprising at least one tube, said drill string being connected to the first element of the uncoupling device, a drilling tool, such as a bit, for drilling a geological formation, the drilling tool being connected to the second element of the uncoupling device, and a device for retaining the drill string, at the drilling wellhead, suitable for controlling the movement up and down of the drill string in the wellbore.
 13. System according to claim 12, wherein the uncoupling device comprises at least one displacement sensor for determining the position of the second element with respect to the first element over time so as to obtain the feed rate of the second element with respect to the first.
 14. System according to the claim 13, wherein the uncoupling device comprises a rotation, thrust measurement and torque measurement sensor for estimating the resistance of the drilled rock and the degree of wear of the drilling tool by means of a cutting model.
 15. System according to claim 12, wherein the uncoupling device comprises at least one displacement sensor for determining a position of the second element with respect to the first element, wherein the system comprises transmission means for transmitting said position of the second element to the retaining device for controlling a retaining effort of the drill string.
 16. System according to claim 15, wherein the retaining effort of the drill string is increased if the position transmitted to the retaining device indicates that the second element is in the vicinity of the first element, and the effort of the drill string is reduced if the position transmitted to the retaining device indicates that the second element is far from the first element. 